The detail was revealed earlier this week when D&D Lead Designer Mike Mearls was asked about the matter on Twitter. "The person who needs to do the final approvals on them is serving on a jury that will take another 4 or so months," Mearls confirmed. "Sorry!"

That's a completely reasonable hiccup in development, even though four months feels like a long time to wait. At least releases like the Eberron update guide will give players a place to start for now. Hopefully by the time we're all finished with the Elemental Evil campaign we'll be able to dive into some classic D&D worlds.